dcook@isis.cs.du.edu (david jeffry cook) (10/23/90)
I am responsible for designing a modem type device and can not find the actual frequencies used for Mark and Spacesignalling Ifor 300, 1200,2400,4800, and 9600 baud or Bps modems. any help would be appreciated!!! David Cook Cook Communications Corporation Denver Colo dcook@nyx.du.colorado.Education
tnixon@hayes.uucp (Toby Nixon) (10/24/90)
In article <1990Oct22.183418.11965@isis.cs.du.edu>, dcook@isis.cs.du.edu (david jeffry cook) writes: > I am responsible for designing a modem type device and can not > find the actual frequencies used for Mark and Spacesignalling Ifor > 300, 1200,2400,4800, and 9600 baud or Bps modems. any help would be > appreciated!!! First of all, please be aware that your mailer is sending out your messages with no RETURNs at the end of lines -- only at the end of paragraphs. This blows away some other people's programs! Each line of the message should go out properly terminated, even if you're using word wrap during message composition. Now, to your question: It is only at 300bps that different frequencies are used for Mark and Space. These are different depending on whether you're using Bell 103 (in the USA) or CCITT V.21 (everywhere else). There's different pairs depending on whether you're the originator or answerer, too. Which do you want? At all higher speeds, Frequency Shift Keying is not used. The modem transmits on a single frequency carrier, and changes the PHASE of the signal (at 1200 bps), or a combination of the PHASE and AMPLITUDE of the signal (at higher speeds) to indicate different bit values. At 1200 and 2400, the modems use "frequency division" (send and receive at different frequencies), but at 4800 and 9600 (at least, in V.32 modulation) they send and receive on the SAME frequencies, and use echo cancellation to differentiate the received signal from the transmitted. Anyway, it's not nearly as simple as you might have thought. Do you need all of the details of how these modems work? I can give you the references to the Bell and CCITT standards. But the easiest way to build a modem is to buy the chips from a company like Intel or Sierra or Silicon Systems or Rockwell (or a number of others), rather than try to do it yourself from scratch. -- Toby -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
gcarter@globey.cs.wisc.edu (Gregory Carter) (11/03/90)
Mmm, its been a little whlie since I was on this topic, but I do believe for 300 baud the tone asignments are: The seperation freq's are 100Hz apart with a line of symetry of 1170. A SPACE is 1070 and a MARK is 1270. This is originate of course. For autoanswer it is also 100hz with a symetry line of 2125Hz, here a SPACE is 2025 and a MARK is 2225. Well, thats all I know without getting into specifics...which would be for 1200,2400, Two level Phase Shift Keying, Quadrature four Phase PSK, Differential Phase Shift Keying, Quadrature Amplitude Modulation QAM. Look under those topics for a good explanation, Otherwise check out C Programmers Guide to Serial Communications, by Joe Campbell Published by Howard Sams Co. This book has more than anybody wants to know about serial communications, its 650 pages long and I have read it twice and STILL don't understand everything in the book. --Gregory **No fancy footers, just an undergrad, no degree. But I BROWN NOSE VERY WELL.